Effect of synthesized zinc stearate on the properties of natural rubber vulcanizates in the absence and presence of some fillers

Abstract

Zinc stearate was synthesized by precipitation method through two steps; neutralization of stearic acid by sodium hydroxide then double decomposition using zinc sulphate to precipitate zinc stearate. Mass balances of the two steps were calculated and the physical properties of the prepared zinc stearate were measured and compared to standard. It was characterized and incorporated it into natural rubber in the absence and presence of some filler through mixing process of rubber. The vulcanization process was carried out at 142 °C. The rheological properties of natural rubber mixes were measured using oscillating disc rheometer. The plysico-mechanical properties of the vulcanizates were determined using tensile testing machine. It was found that, partial and complete replacement of synthesized zinc stearate instead of the conventional zinc oxide and stearic acid; enhanced the physico-mechanical properties of natural rubber. The measured reinforcing parameter value α f can be arranged according to the type of filler as follows: HAF > Hisil > CaCO 3 > Ca 3 ( PO 4 ) 2 > BaSO 4 > Talc The highest value of α f represents the strength of filler and consequently the reinforcing effect of carbon black (HAF) filler while the lowest value of α f was observed for Talc which show moderate reinforcing effect of Talc. The scanning electron microscope study showed high surface homogenity and good dispersion of zinc stearate through natural rubber chains in case of the vulcanizate containing 9 phr zinc stearate without filler. The investigated natural rubber vulcanizates tolerated thermal oxidative aging at 90 °C for 7 days.